178 



SCIENCE. 



[N. S. Vol. VIII. No. 189. 



that the latter is a specialized form of the 

 former. 



The place of separation is interseptal ; 

 the anterior half-segment produces an anal 

 segment and a preanal, undiiferentiated, 

 segment-forming zone ; the posterior half 

 forms four cephalic segments and the pros- 

 tomium. 



The ectoderm by ingrowths between the 

 longitudinal muscle bands produces in the 

 posterior zooid the brain, the circumoesoph- 

 ageal connective, the sub-oesophageal gan- 

 glia, four pairs of ventral bristle-sacs and 

 two latero-ventral invaginations, the walls 

 of which contribute to the formation of the 

 buccal wall. The floor and roof of the 

 mouth are also ectodermal, but are formed, 

 upon the separation of the zooids, by the 

 free mid-dorsal and mid-ventral margins of 

 the body wall, which are drawn into con- 

 tact with the entoderm by muscular action. 

 In the anterior zooid the ectodermic in- 

 growths fuse with one another and with 

 mesodermal elements to form an undifferen- 

 tiated zone, from which new segments are 

 added to this zooid. The nerve cord, the 

 dorsal and ventral bristle sacs, and the per- 

 ipheral portions of the nephridial organs, 

 are contributed by the ectoderm. 



The entoderm increases in thickness 

 thi'oughout the bud-zone by the multiplica- 

 tion of sub-epithelial cells. In two regions 

 this becomes pronounced. In the posterior 

 zooid a thick wall of long, columnar, ciliate 

 epithelial cells is produced, surrounding 

 the old tube. This outer wall soon becomes 

 separated from the old wall by a distinct 

 space, the lumen of the new pharynx. An- 

 teriorly this new pharyngeal wall becomes 

 continuous with the ectodermal portion of 

 the wall of the mouth ; posteriorly it ex- 

 tends to the dissepiment bounding the bud- 

 zone. The wall of the old gut continues 

 functional until the individuals separate, 

 and is then detached and swallowed. In 

 the anterior zooid there is a thickening of 



entoderm immediately in front of the future 

 plane of division. This arises in a way 

 wholly similar to the pharyngeal wall, and, 

 like it, becomes separated from the wall of 

 the gut. It is cilitated and is destined to 

 become the wall of the pavilion, which 

 probably subserves a respiratory function. 

 From the mesoderm arise new muscular 

 fibres, blood vessels and dissepiments. 



Effect of Temperature on Growth of Tadpoles. 



(Abstract.) By T. W. Galloway. 



Tadpoles of Eana, Amblystoma and Bufo 

 were reared, without other food than was 

 contained in the eggs, under different tem- 

 perature conditions (varying from + 16° 

 to + 25°C.), to an age of 30 to 70 days. 

 Through a comparison of the total weight, 

 the dry weight, the amount of water 

 and the ratio of the dry weight to the 

 total weight, the following conclusions 

 were reached : (1) Increase of tempera- 

 ture, within the above limits, accelerates 

 cleavage and the rate of imbibition of 

 water (especially the latter), but does 

 not appear to produce any definite 

 change, either of increase or decrease, of 

 formed substance ; (2) organisms reared in 

 the warmer conditions tend to attain a 

 slightly higher maximum percentage of 

 water than those subjected to lower tem- 

 peratures; and (3) individuals reared for 

 sometime in a low temperature showed, 

 after transfer to a higher temperature, a 

 greater rate of imbibition of water than 

 those kept from the beginning in the 

 warmer chamber. 



Structure and Development of the Antennal 

 Glands in Homarus americanus. (Ab- 

 stract.) By F. C. Waite. 

 The adult organ consists of three por- 

 tions, an endsac, labyrinth and vesicle. 

 The endsac lies spread over the dorsal face 

 of the labyrinth, and closely applied to it. 

 These two portions of the gland are in com- 

 munication at one point only, which is in 



